1. Field of the Invention
The present invention relates to articles and methods for blocking a flow of material within a bone canal, and, more particularly, to canal plugs and associated methods.
2. Description of Related Art
In procedures in which an implant is placed within a bone canal it is typical to anchor a distal portion of the implant with a cement material that flows in a liquid state and hardens upon drying. Once sufficient cement has been added under pressure to the canal and permitted to partially dry, the implant distal end is inserted, with a complete drying of the cement achieving a permanent fixation within the canal. In such procedures it is undesirable for the flowing cement to continue beyond the desired implant site, under pressure from the insertion of the implant, since such a displacement would lessen the amount of cement available to achieve optimal fixation.
Such procedures include hip replacement, which involves cutting off the head of the femur, opening the top of the femur, and cleaning out the canal to a length commensurate with the length of the implant stem. The canal is then plugged at the bottom of the cleaned-out space, the implant stem is inserted, and cement is forced around the pin to keep it in place.
The femoral canal plugs used at present are typically provided in a set of incrementally sized high-molecular-weight polyethylene truncated cones that are force-fit into the canal. However, femoral canals are not circular in cross section, but are oval or elliptical. Using a plug having a circular cross section thus leaves gaps surrounding the plugs through which cement may leak and extrude down the canal potentially as far as the knee region.
A further problem can occur with a plug that does not conform sufficiently well to the canal: With modern cement techniques, under the high pressures with which the cement is forced into the canal, plug "blowout" can occur, forcing the plug below the desired location. If these cases go on to require revision surgery at a later time, which occurs with a frequency of 5-10%, a very extensive and potentially destructive (relative to bone stock) operation must be undertaken to remove the cement.
Several intramedullary bone plugs are known in the art, including those that have elements adapted to change shape or expand after insertion into the canal. Among these are those disclosed by Seidel et al. (Eur. Pat. Appl. No. 0 006 408), Haynes (U.S. Pat. No. 4,697,584), Hardinge (U.S. Pat. No. 4,276,659), Swanson (U.S. Pat. No. 4,302,855), Weber (U.S. Pat. No. 4,447,915), Murray (U.S. Pat. No. 4,625,722), Frisch (U.S. Pat. No. 4,686,973), Kummer et al. (U.S. Pat. No. 5,092,891), Wilson (U.S. Pat. No. 5,383,932, and Huene (U.S. Pat. No. 5,531,792).
None of the plugs thus far disclosed, however, adequately conforms to the cross-sectional shape of a bone canal without leaving gaps through which cement may extrude and also is unlikely to experience "blowout."